JPS5951051B2 - information reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an information reading device that optically reads information such as video or audio information.

A conventional device of this type is shown in FIG.

In the figure, 1 is a light source such as a laser that generates a light beam, 2 is a concave lens for converting the light beam from the light source 1 into diverging light,
3 is a deflector that deflects the light beam converted into diverging light by the concave lens 2; 4 is a condenser lens that condenses the light beam deflected by the deflector 3; and 5 is a condenser lens that condenses the light beam deflected by the deflector 3. This disk 5 is a recording medium (hereinafter abbreviated as a disk for explanation taking a disk-shaped recording medium as an example) that is irradiated with a light beam, and this disk 5 has a structure in which information such as video or audio information can be optically read. A flat record carrier on which tracks are recorded.

In this information reading device, light from a light source 1 is transmitted through a concave lens 2.
The light beam is converted into a diverging light beam by a radiator, and is focused onto a track of a disk 5 via a deflector 3 and a condensing lens 4. It is designed to read the information recorded on the track.

During this reading, the disk 5 is rotating as shown in FIG. 1, and the light spot scans over the tracks of the disk 5, allowing information to be read one after another. At this time, the light spot must be scanned so as not to deviate from the track. As information becomes denser, the track spacing becomes closer, making it impossible to track with mechanical precision due to disk eccentricity. Therefore, the positional deviation between the track and the light spot is detected by some method, and the deflector 3 is driven based on the signal, and the direction of the light beam incident on the condensing lens is changed so that the condensed spot can correctly scan the track. It is very controlled. In the conventional device described above, when reading information, in order to eliminate deviations in light convergence caused by vibrations of the surface of the disk 5 in the optical axis direction due to the rotation of the disk 5, a speaker is used, for example, in conjunction with the vibrations of the disk 5. Adjustments are made by moving the condensing lens 4 in the optical axis direction by a method utilizing the principle of the voice coil.

For this reason, it is desired that the condensing lens of the conventional device be small and lightweight, but generally an objective lens of a microscope is used. This lens is expensive, and since it is a combination of multiple lenses, it is not ideal in terms of size and weight. In contrast, small, lightweight, and inexpensive lenses, such as gradient index lenses, have recently become commercially available, and if this type of small lens is used as a condenser lens, the control device for condensing light can be made smaller. Realized.

However, the above-mentioned small lens is the condensing lens 4 shown in FIG.
If this is replaced with the configuration shown in FIG. 2, the following new problem will occur. That is, in order to control the condensing spot so that it does not deviate from the trap, the inclination of the deflector 3 is changed to deflect the light beam, but as shown in Fig. 2, the small condensing lens 6 has a small incident surface, so it is difficult to deflect the light beam. The disadvantage is that the emitted light rays tend to deviate from the incident surface of the small condenser lens 6, making it practically useless. Therefore, in the conventional device, there is a limit to the miniaturization of the condensing lens, and as a result, the control device for condensing the condensing light must also be large and complicated. The present invention was made in order to eliminate the above-mentioned drawbacks of the conventional apparatus, and aims to provide an economical information reading apparatus by making it possible to use a small condenser lens.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows a schematic configuration of an embodiment of an information reading device according to the present invention. In the figure, 7 and 8 are convex lenses that convert the light beam from the light source 1 into convergent light with a wide beam diameter;
Reference numeral 9 denotes a first condenser lens for condensing the light beam onto the disk 5, and numeral 10 denotes a second condenser lens for making the light beam from the deflector 3 enter the incident surface of the first condenser lens 9.

In this embodiment, the light emitted from the light source 1 such as a laser is
It is converted into a focused beam with a wide beam diameter through convex lenses 7 and 8, and is directed onto the disk 5 via a beam deflector 3 such as a galvanic mirror, a second condensing lens 10, and a first condensing lens 9. The light is focused. In addition, beam deflector 3
and the second condensing lens 10 is a, the distance between the second condensing lens 10 and the first condensing lens 9 is b, and the focal length of the second condensing lens 10 is f. Then, the respective positional relationships are arranged so as to satisfy the following formula.

That is, a plane passing through the center of deflection of the light beam deflected by the beam deflector 3 and perpendicular to the optical axis of the second condensing lens 10 is in a conjugate relationship with the plane of incidence of the first condensing lens 9. It's getting old. Next, the operation of the reading device having the above configuration will be explained.

The light from the light source 1 passes through two convex lenses 7 and 8,
The light is converted into a focused light beam with a wide beam diameter, and is once focused through a beam deflector 3. This focused point is the second
The diffused light is converted into parallel light by the second condenser lens 10 and then enters the first condenser lens 9. , the light is condensed by this first condensing lens 9 and irradiated onto the disk 5. In this case, the positional relationship between the beam deflector 3, the second condensing lens 10, and the first condensing lens 9 is arranged so as to satisfy equation (1). On the other hand, the beam reflecting surface of the beam deflector 3 and the incident surface of the first condensing lens 9 form a conjugate relationship. That is, even if the beam is deflected by the beam deflector 3, the incident position on the incident surface of the first condenser lens 9 through the second condenser lens 10 remains unchanged. Therefore, the drawback that the beam deviates from the lens when it enters the small condensing lens 6 as shown in FIG. 2 is eliminated, and the loss caused by the vignetting of the light is eliminated. Furthermore, as for the means for detecting information and the mechanism for focusing, known devices (not shown) can be used as they are, as explained with reference to FIG.

In the above embodiment, after passing through the beam deflector 3, the light beam from the light source 1 is condensed before reaching the second condensing lens 10, and then the beam is condensed through the second condensing lens 10. Although the light beam is converted into parallel light and made incident on the first condensing lens 9, even if the incident light is changed into diffused light or converged light, the focal length, positional dimensions, etc. of the first condensing lens 9 cannot be changed. By changing the configuration, it is possible to provide the same function as in the above embodiment.

When using a gradient index lens as the first condensing lens, by changing the length of the cylindrical lens, it is possible to condense even non-parallel incident beams onto the disk 5. can. As described above, according to this invention,
The optical system is arranged so that the beam reflecting surface of the beam deflector and the incident surface of the first condensing lens form a conjugate relationship.
This provides the effect that the beam does not deviate from the small condensing lens with a small aperture. This makes it possible to use a small, lightweight, and inexpensive lens, typically a gradient index lens, as a lens for focusing the beam on the disk surface, and the control device for focusing can also be made smaller. Not only is this possible, but it is also economically effective.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional information reading device, FIG. 2 is a diagram illustrating the drawbacks that occur as a result of some improvements in the conventional information reading device, and FIG. 3 is a schematic diagram showing an information reading device according to an embodiment of the present invention. It is a schematic diagram showing a reading device.

Claims (1)

[Claims] 1. A light source, a deflector that deflects the light beam from the light source, a first condenser lens that focuses the light beam deflected by the deflector onto the recording medium, and a space between the first condenser lens and the deflector. The deflector is arranged such that the center of deflection of the light beam deflected by the deflector and the incident surface of the first condenser lens have a conjugate relationship, and the light beam deflected by the deflector is directed to the first condenser lens. An information reading device comprising: a second condenser lens that condenses light onto an incident surface of the lens; and a detection means that detects transmitted light or reflected light from the recording medium.